A trocar assembly generally includes two major components, a trocar body and an obturator. The trocar body typically includes a cannula having a cylindrical configuration and a valve housing. When operatively disposed, the cannula of the trocar body extends across a body wall, such as the abdominal wall, to provide access into a body cavity, such as the abdominal cavity. The obturator typically includes an elongate body having a sharpened distal tip. Placement of the trocar body in the operative position is facilitated by the obturator and its sharp distal tip which actually punctures and penetrates the tissue forming the body wall.
The elongate body of the obturator is typically mounted in the trocar body with the sharp distal tip extending beyond the distal end of the trocar. As the trocar is pushed or otherwise moved through the body wall, the sharp distal tip functions to cut the tissue and provide and opening for the trocar. Once the trocar is operatively positioned, the obturator can be removed from the trocar body leaving the cannula to provide working-channel access into the body cavity.
It is certainly one of the primary purposes of the obturator to provide a sharp distal tip to facilitate the cutting of body wall tissue as the assembly penetrates the body wall. However, of equal importance, is the need to insure that the cutting stops once the body wall has been penetrated. It has been found that a relatively large force is required to cause the sharpened tip of an obturator to penetrate the body wall. However, once the sharpened tip penetrates the body wall, resistance to penetration is removed and the sharpened tip of the obturator is suddenly free to reach into the body cavity and cause additional cutting. Failure to stop this cutting action can result in considerable damage to interior organs and other tissues within the cavity.
In an effort to avert these dangers to the patient, trocars have been developed with a variety of safety features and devices. One common safety device includes a spring-loaded tubular safety shield which surrounds the shaft and the sharpened tip of the obturator. The distal end of the tubular shield presses against the skin as the sharpened tip of the obturator penetrates the body wall. When the obturator has formed an opening in the body wall of sufficient size that the tubular safety shield can pass therethrough, resistance to the movement of the tubular safety shield is removed. This allows the safety shield to spring forward and cover the sharpened tip. Once the sharpened tip is covered, the internal tissues and organs are protected from inadvertent cutting. An example of a trocar including such a safety shield is described and claimed in U.S. Pat. No. 4,535,773.
Unfortunately, trocars having these spring-loaded tubular safety shields require larger incisions. Particularly, the incision formed by the obturator generally must extend to the outer diameter of the tubular shield before the resistance of the tissue pressure is decreased to allow the shield to spring forward. These tubular shields also possess a relatively large mass which has required considerable time to move the shield into the forward or safety position. Tubular shields have also left a relatively large distal opening which has provided some access to the sharped tip of the obturator.
The sharpened tip of the obturator typically includes a blade having a symmetrical triangular form. These blades tend to form an opening which results in a wound consisting of three cuts each radiating from a central puncture or penetration point. While it is generally agreed that this blade configuration provides minimal entry force, it has been of recurring concern that the resulting wound can result in herniation, as well as other complications associated with wound closure and healing.
Obturators having single blade configurations have also been developed. These single blade obturators penetrate the body wall through a single incision which reduces the concerns about wound herniation, closure and healing. An example of an obturator having a single-blade configuration, is disclosed and claimed by Schwemberger et al. in U.S. Pat. No. 5,609,604. The obturator of this patent has a conical distal tip that is axially slotted to receive a planar blade which is movable between a distal exposed position and a proximal retracted position. However, the relatively heavy blade and supporting mechanism add significantly to the actuation time required for retraction. This actuation time leaves the blade exposed, potentially allowing undesired and unnecessary cutting to continue. This configuration also fails to provide an incision which accommodates the full diameter of the obturator. As a result, insertion forces required to penetrate the body wall tend to be relatively high.